Building a Floating Net Platform for Lobster 'grow-out' Aquaculture

[jamesmusslewhite]

   This is a spin-off thread from the 'Building a Small Lobster Hatchery here in the Philippines' http://www.philippines-expats.com/topic/26117-building-a-small-lobster-hatchery-here-in-the-philippines/?tab=comments#comment-192173  which will be discussing several types of floating nets and floating cages which I will eventually be constructing to use for the lobster hatchery facility. I will be not only raising lobsters from eggs but will also be raising various saltwater species of fish, crabs, shrimp and assorted shells to be used to feed the lobsters being produced in the hatchery. This need will require several different styles of floating nets and cages. This is why I felt that by grouping these into a separate thread it would help the readers to more easily follow the information while allowing the hatchery thread to remain less cluttered.

   My first net system is a large multi-purposed floating platform which will be used for lobster 'grow-out' aquaculture. We will be purchasing Pueruli and Algal-juvenile size seedstock and will be raising them to 500gram size buyer's market weight. This is what is called lobster 'grow-out' aquaculture. This first floating net platform system though built for open-water lobster 'grow-out' aquaculture, is a design which is adaptable for both freshwater and saltwater 'grow-out' aquaculture.

   When I first sat down to design this platform I knew what I wanted to use it for, and I understood that it would have to meet certain criteria. First I knew that I wanted a (6 meter x 6 meter) floating net-platform. The platform needed to have a large net enclosure capable of performing several different functions at the same time. The platform must be capable of handling the stresses of moderate to heavy wave action (Cat-2 to Cat-3 tropical storm), and capable of being quickly relocate to a more sheltered location in case of typhoons. The frame needed to be constructed out of a durable lightweight medium which is affordable, yet both extremely strong and flexible as to not easily buckle by heavy wave action; which of course made (single-length bamboo construction the best option). And the the platform needed to be constructed with a sufficient height above the waterline to protect the walkways from heavy wave action, and handle the wear from boats which will be lashed to the frame during normal day-to-day usage. Well that certainly seemed easy enough at the time, but it quickly turned into quite a task which took some time to take it from concept to reality. 

.   When I first started sketching out the platform I decided I would look at some examples on the internet to use as an example. Well I quickly discovered that there was actually very little on the internet and what was available offered little in the way of useful information. In fact it became clear that what sketches were on the internet were not actually sketched by someone who had actually built one before, as there lots of artistic license being employed in their sketches. This is the closest drawing off the internet which I could find to the design I was working with in my head.

So I decided to stop looking for assistance on the internet and just start sketching a long series of rough drafts and drawing until something that appeared to be a feasible working design stated to evolve into something that seemed practical. I then sat down and made a working model using plastic straws, bamboo toothpicks and sewing thread and built a prototype.

   I knew that plastic straws reacted similar to lengths of bamboo when stressed, and that the plastic straws displayed a similar flexibility to that of bamboo lengths. This allowed be to build a platform in miniature, which I could easily hold in my hand and twist and flex.

This would allow me to simulate the stresses the platform would most likely encounter during heavy wave action. I would test, discover the flaws in the design and build another straw model and test that one, and so on and so on.

I was able to strengthen those areas in the design which had weaknesses, and trim-down all unnecessary weight while maintaining the integrity of the frame. Eventually I had a simplistic design which was extremely strong but required a minimum of building materials which would help keep the material cost low for the project.          

   I now knew that I had the design just as I wanted. The model also allowed me to already assemble the platform; so I was confident that all the needed bamboo lengths, bracings and sections connecting the 55gal plastic drums to the frame were correct. All the materials had already been collected and the bamboo had been properly dried, so now it was time to assemble this project so we can get it in the water for real. 

[jamesmusslewhite]

   First I had eight 55gal. plastic barrels delivered to the island. It is important that the plastic barrels are food grade and have only contained proteins because you do not want to use any barrel which has been used to contain chemicals. This is because it is not uncommon for plastic drums to leak around the threads of the two plastic bungs. This is because the barrels experience surface stresses caused by the weight of wood or bamboo laid across their surface and the up-welling forces of the water underneath them. There is a certain flexibility to the surfaces of 55gal plastic barrels especially when exposed to direct sunlight as the heat up both on the outer surfaces as well as in the inside. When used for floating platforms the wave movements and the movement of personnel on top of the platform can and often does seep both air and water into and out of the plastic bungs of a plastic barrel. A barrel which was used to contain a concentrated toxin risks leaking toxic contaminates into the environment of your net enclosure. Always ensure the barrels have only been used only to contain food grade proteins, and thoroughly clean inside the barrels. I also suggest that Teflon tape (plumber's tape) is used on the plastic threads of the bungs, and that the plastic bungs are thoroughly tighten to minimize seepage and maximize the buoyancy of the plastic barrels when they are deployed

There has been two large bundles of fresh-cut bamboo delivered to the island. fresh-cut bamboo is moist which makes it more difficult to cut as the moist sawdust tends to bind the saw-blade. I sort through the bamboo lengths to separate and size them. Then I let the bamboo to dry for 2-3 weeks before I start to assemble the floating platform. The reason for letting the bamboo have time to dry is so the bamboo to shrink. If you start lashing together green bamboo it will shrink as it begins to dry. This will loosen the the lashings and weaken the frame. 

   The bamboo was easier to tie in bundles with rope and then pull the tied bundles behind the boat to the island.  

So after all the drawings and the building straw models, it finally reached the time when I could finely start building the beast. I always love starting a new project 

First I start cutting the long lengths so I can build two sides of the platform. The frames which will be placed on top of the plastic barrels will be the first items built and six of these frames will need to be built.

 

 

[jamesmusslewhite]

 

[jamesmusslewhite]

   The bamboo lengths are cut to the desired lengths and lashed together using #150 nylon line. A paddle bit is used to drill a small hole in the bamboo and the #150 nylon line is threaded through the bamboo sections and then lashed together. This makes a strong union and is the same technique used to lash together the outriggers on boats. It was paramount that at every hole drilled (using a sharp chisel) we carve a bevel to remove that sharp 90 degree edge lip of the drill hole. If this was not done than it would be almost impossible to properly tighten the nylon line which is threaded through the bamboo lengths, also when trying to thoroughly tighten the nylon line (without being beveled) the sharp edge of the drilled hole would severed at the drilled holes. 

   My brother-in-law showed me several times, and each time there was the same result. He wanted to show me the importance of carving these bevels so we both insure that these bevels were always carved. But the drilled edge inside the bamboo does not need to be beveled (only the outside edges) even when stacked and lashed together. Only were the nylon line will be bent to a 90 degree angle.

 

 

[jamesmusslewhite]

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[jamesmusslewhite]

Well at the time of this photo we had two sides of the frame already prepared for the next phase of the construction, so it was time to carry them outside of the yard where we could begin assembling the main frame body. We had a nice location which was accessible to electric, had fair shade coverage and was close to the shoreline. I was excited after all the time designing, building and testing models and having to wait until it was time to finally build the prototype. This was actually the first time I could see true full-size dimensions of the platform. The inner net area will be slightly over 5.8 meter x 5.8 meter (19 feet x 19 feet).

The concept is simple. Place one of the two sides which has already been assembled next to the shoreline and the other up on land. Then place 3 long lengths of bamboo at each corner. This was to make it easy to lineup the edges of the bamboo lengths, and use a square to insure we were working with 90 degree angles. Then we were able to lash the long lengths to the squared side at the edge of the shoreline.

   Each side of the platform serves as a walkway, and each of the four walkway will be constructed using 13 long lengths of bamboo This will give the platform incredible strength, but will also be flexible and durable which in important during heavy wave action. Once the first corner is lashed then we move to the next corner and do the same.

   All the lashings is done using a quality (heavy duty) #150 nylon monofilament line. It will hold up to the tropical heat and intense direct sunlight UV, and will surely outlast the bamboo which it is tasked with holding together. The life of the bamboo platform should be between 2 - 3 years.

   once the 3 long lengths on one corner was thoroughly lashed together, we then moved to the other corner.

   And we had moved on to the second corner. Now I bet that at this point some of the viewers have noticed those small trees, and are wondering what kind of a carpenter worth his weight would build a square shaped platform in the middle of trees? I am certain that those local folks watching us had that though, and figured we might have to be cutting some trees. But there was a method to our madness as you will see in the next photo .

   The second side was merely a large worktable at this point. Once we had both corners of the shoreline properly squared and completely lashed together, we simply pushed the second side forward. Most of the construct will be pushed into the water to float as the construction continues. Then when needed the second side will simply be picked up and carried to the shoreline side of those small trees and lashed to the main frame. The whole frame then can be easily rotated as we work on all the braces. As my wife operates a small daytime resort on the island, doing the construction in this manner allowed us to stay out of the way of her customers, but also allowed us to continue working pretty much undisturbed. The humorous thing is when we take a brake either adults want climb on it to take selfies and glamor shots, or the small children want to climb out on on it to dive in the water. But when we are working on the platform they leave us alone.

 

[jamesmusslewhite]

   This photo shows how the second side became a temporary second work top.

then as we pulled the first side into the water, we carried the second side and placed it in the same location as the first side previously was. then the six long bamboo lengths were lifted up on top of the second. Meaning no trees died while making this forum thread.

   now we simply positioned, aligned and squared the long bamboo lengths as we lashed each of the remaining two corners. Bamboo can be a difficult building material as lengths are rarely straight, are thicker at one end than the other and are inconsistent as to size.  

   You want to always want to cut bamboo close to the not as it strengthens lengths being lashed, if you cut the knot off then you have a narrow-walled tube section which ca easily crush, collapse, split or splinter.  Unlike lumber which can be cut at exact lengths and has a consistent thickness, each length of bamboo is unique as the length, thickness, size and circumference. The best you can do is get grenade-close. You can not make bamboo conform to you, rather your going to have to work with what bamboo gives you. But bamboo is inexpensive, light-weight, strong and the best material for this task.

   We still have a long way to go before this project is complete

we still have plenty of bracing  which needs to be added, mounts for two more 55gal. plastic barrels, railings, two ladders,and other features before we even start dealing with making the nets. I

   So I hope you have found the thread interesting so far, as we still have a lot more to cover.

[jamesmusslewhite]

Well I figured that I keep mentioning the lashing together of the bamboo lengths with a #150 nylon monofilament line, so I thought it best to actually show what us being used.  

this is a quality line which I was fortunate to discover being sold here in Surigao City.

the locals call it #150 but it is actually a 1.90mm line which is test 150lbs. rated

as we finished lashing the six long lengths to the two corners the time has come to start adding the needed braces which will give the frame strength. 

There is quite a bit of bracing which must be added and we want to keep the frame as square as possible as we work our way around the frame.

the bamboo sections must be held tightly as the lengths are tightly lashed together. It is certainly a a two man task to do it correctly as it is paramount that every lashing is a tight as possible..

 

[jamesmusslewhite]

 

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[jamesmusslewhite]

   There are two barrels which must have an additional length of bamboo added as a spacer to allow the barrels to sit lower. This is needed so all of the barrels will sit in the water at the same level. The issue is possible wave action damage to the frame ii either of these two bamboo spacers were to be knocked loose. To avoid this from happening we will use bamboo dowels. These dowels are hammered through both the long bamboo lengths and the bamboo spacer lengths. These bamboo dowels are quite easy to make with a saw and a sharp chisel.     

A hole is drilled through the two lengths of bamboo, and then the bamboo dowel is driven through the hole like a long spike. And once lashed together with the nylon line there are firmly bound together. 

When the time comes to add these two barrel assemblies to the framework, they will both sit on sound footing as these spacers will not twist or slip if hit by waves.

   And now that we have the the corner braces properly lashed in place, we know that the frame can now be pulled to the sheltered side of the island, without fear of the frame folding or being knocked off square. Once the frame is safely relocated and tied into place we inspect the frame to insure it is squared at each corner.

   As you can see in the photo we got up before sunrise the next morning so we could begin adding the rest of the frame bracing. It was a rather nasty overcast morning but we were not going to this dampen our spirits. .